Method of treating alloys



NORMAN BQPILLING, or WILKINSBURG,

HOUSE ELECTRIC & MANUFACTURING COMPANY, A

VANIA.

PATENT OFFICE.

PENNSYLVANIA, ASSIGNOR TO WESTING- CORPQRATION 0F PENNSYL- METHOD or TREATING ALLOYS.

No Drawing. Application filed September To all whom it may concern:

Be it known, that I, NORMAN B. FILLING, a citizen of the United States, and a resident of Wilkinsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Methods of Treating Alloys, of which the following is a specification This invention relates to metals and alloys, more particularly to the production of resistor metals and alloys having high negative temperature coeflicients of electrical resistance.

Metals and alloys of this type may be utilized in various devices, such as meters and other electrical measuring instruments. An indicating meter generally comprises a copper coil which is influenced by a magnetic field and caused to oscillate to thereby indicate certain electrical quantities. Owing to temperature changes, the amount of oscillation or deflection of the coil varies and to neutralize this variation it has been customary to insert a resistor of a material having a low temperature coeflicient to correct for the error introduced by the large positive coeflicient of the copper coil and the negative coefficient of elasticity of the restoring.

spring.

The insertion of this resistor necessarily diminishes the. sensitiveness of the meter,

.and it is'among the objects of this invention to provide a metal or alloy having a high negative temperature coefficient of electrical resistance which shall effect this co-mpensa tion with a lower ohmic value of resistance and a correspondingly smaller loss of sensitiveness.

In my copending application, Serial No. 585,855, filed Sept. 2, 1922, for alloys, I have described a nickel-copper alloy which has a high negative temperature coefficient and is suitable for this work. However, I have found that even this alloy, after the temperature coefficient thereof had been increased by cold working, ris not entirely stable, and temperature changes afiect the same. It is, therefore, another object of my invention to provide a method of treating metals and alloys, of which the above is an example, which shall increase the negative temperature coefficient thereof and stabilize the same over a predetermined range of temperature.

In carrying the objects of my invention 2, 1922. SerialNo. 586,026.

into effect, I provide a metal or alloy of any suitable type having, preferably, a negative temperaturecoefiicient of resistance and so treat the same as to change the temperature coelficient thereof in the negative direction. This results, in the case of a metal or alloy having an initially positive temperature coefficient, in diminishing its temperature co efficient; and it causes the negative temperature coefficient of metal or alloy to still further increase in the negative direction.

This is accomplished by subjecting the metal 'or alloy to a cold Working process, such as drawing, rolling, forging and the like, whereby the cross-section of the metal ,or alloy is reduced. Apparently, the reduction in the temperature coeflicient is directly proportional to the reductionin the cross-sectional area of the metal or alloy. I have applied this method of working to a pure nickel-copper alloy by subjecting the same to successive reductions in a wire drawing machine without intermediate annealing and have thereby increased its nega tive temperature coeflicient. I have found that, for each 10% reduction in cross-sectional area of the alloy, the negative temperature coefficient was increased about 8%. For alloys of relatively low temperature 00- eflicient, the percentage increase is much A higher.

Such a cold Worked and hardened metal or alloy is physically unstable, and the electrical resistance, which is also increased by cold Working, will sufler permanent small changes if the temperature of this metal is raised, even momentarily, above the final drawing temperature at which the wire was made. Such changes are undesirable in electrical measuring instruments. I have found that, by giving the cold-drawn wire a brief annealing treatment at a temperature of'200 0., the resistance will quickly diminish to a stable value without change in temperature coefficient. After this stabilizing treatment, the resistor may be safely heated to temperatures below the stabilizing temperature without permanent change in resistivity. h

I generally 'heat the drawn metal to 200 (1., since the temperature coefiicient is not changed materially by heating up to this maximum temperature. Furthermore, 200 is above the temperature which is utilized in soldering the wires to leads and terminals.

Therefore, by annealing at 200, I subject the material to the maximum temperature it would receive in manufacture and service, and I thereby stabilize the material to this temperature. 'In some cases, it may not be necessary to stabilize at such a high temperature and lower temperatures, for instance 100 0., may be utilized.

The following is an example of the change in characteristics of a 50% nickel-copper alloy which was subjected to this treatment.

'The ordinary alloy, after annealing, had a tion thereof, it is not confined to the alloy described above. I believe that my method is of general utility and is applicable to other alloys, such as nickel-copper-manganese alloys, as a means of increasing anoriginally negatlve temperature coefiicient or reducing a positive temperature coeflicient. My invention is, therefore, to be construed broadly, except as limited by the claims appended hereto.

I claim as my invention:

1. The method of treating alloys having a coefficient of resistance zthat continuously approaches zero as the material is coldworked which comprises cold-working said material and heating to a temperature not higher than 200 C. for diminishing the resistance thereof.

2. The method oftreating alloys having a coeflicient of resistance that continuously approaches zero as the material is coldworked which comprises cold-working said material and heating to a temperature not higher than 200 C. for stabilizing the resistance thereof.

3. The method of treating alloys having a' coefficient of resistance that continuously approaches zero as the material is coldworked which comprises cold-working said material and heating to a temperature not higher than 200 C. for establishing the minimum stable resistance in said alloy.

4. A method of treating alloys which con-l sis'ts in cold working the same to reduce the cross-sectional area and to reduce the temperature coefficient of resistance thereof and annealing the worked alloy at a maximum temperature of about 200 C. to stabilize the same.

5. A method of treating alloys having a negative temperature coefficient of resistance which consists in cold working the same to reduce the cross-sectional area and to increase the negative temperature coeffi cient of resistance thereof and annealing the worked alloy at a maximum temperature of about 200 C. to stabilize the same.

6. A method of treating nickel-copper alloys which consists in cold working the same to reduce the cross-sectional area about 90% and thereby providing an alloy having a NORMAN B. FILLING. 

